Aromatic polyimides are well known as polymers with outstanding mechanical properties and high temperature capabilities. The extreme processing conditions and expense of these materials has limited their widespread adoption as matrix materials for structural composites. In recent years, significant efforts to develop polyimides that are economical, that exhibit a high glass transition temperature, Tg, and that are readily processable, have met with limited success.
Composite systems, designated Avimid.RTM. K (E. I. du Pont de Nemours), employing matrices based on pyromellitic dianhydride and extended ether diamines have recently been described (A. R. Wedgewood, SAMPE Tech. Conf. 24, p T385, 1992). These linear polymer matrices have very attractive mechanical properties. The polymers have high melt flows at modest processing conditions, even after full polymerization and devolatilization. Thus, these materials are compatible with composite molding processes featuring melt consolidation of devolatilized prepreg plies. Such melt processes produce inherently high quality laminates (U.S. Pat. No. 5,059,273). The dry glass transition temperatures of the neat resins from Avimid.RTM. K range from 220.degree. to 255.degree. C. Saturation with 80.degree. C. water yields a wet Tg range of 190.degree.-205.degree. C.
The current invention provides novel polyimides which have dry/wet Tg and flow at least equivalent to Avimid.RTM. K with good thermal oxidative stability and mechanical properties. The invention also offers the potential of a more economical product by replacing some of the expensive components of the state of the art polymer with less expensive ingredients.